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Wireless Telemetry for Electronic Pill Technology

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					   Wireless Telemetry for Electronic Pill Technology
                                    Mehmet R. Yuce, Tharaka Dissanayake, Ho Chee Keong
                       School of Electrical Engineering and Computer Science, The University of Newcastle,
                            University Drive, NSW 2308, Australia. mehmet.yuce@newcastle.edu.au

Abstract—This work will address the challenges to facilitate the
development of a high capacity radio system for a small,
miniaturized electronic pill device that can be swallowable or
implantable in human body in order to detect biological signals
or capture images that could eventually be used for diagnostic
and therapeutic purposes. In addition to reviewing and
discussing the recent attempts in electronic pill technology, a
wideband (UWB) telemetry system aimed for the development
of an electronic pill will be presented in this paper. We have
successfully realized more than half a meter UWB link under
conditions emulating an implant

                        I.    INTRODUCTION
    Recent development in electronic pill technology requires
the integration of more complex systems on the same platform
when compared to conventional implantable systems. A small               Fig. 1. A wireless endoscope monitoring system.
miniaturized electronic pill can reach areas such as small
intestine and deliver real time video images wirelessly to an
                                                                         electronic pill technology, a wideband telemetry system aimed
external console. Fig. 1 shows a wireless endoscope (i.e.
                                                                         for the development of an electronic pill will be presented in
electronic pill) for a medical monitoring system. The device
                                                                         this paper. We have successfully realized more than half a
travels through the digestive system to collect image data and
                                                                         meter UWB link under conditions emulating an implant
transfers them to a nearby computer for display with a
distance 1 meter or more. A high resolution video based
capsule endoscope produces a large amount of data, which                     II.    WIRELESS TELEMETRIES USED IN ELETRONIC PILL
should be delivered over a high capacity wireless link.                      There are plenty of publications describing the current
   Since its early development [1]-[3], wireless endoscope (i.e.         trend on wireless endoscopes and technologies. One of the
electronic pill) designs have been based on narrow band                  recent articles given in [7] gives a good history of capsules
transmission and thus have limited number of camera pixels.              from their early development to clinical implementation. The
One of current state-of-the-art technologies for wireless                design of wireless capsules started around 1950s. Since then,
endoscope device is commercially available by the company                they have been called as endoradiosondes, capsule, smartpill,
“Given Imaging” [4]. The pill uses the Zarlink’s RF chip [5]
                                                                         electronic pill, wireless capsule, wireless endoscopy, video
for wireless transmission based on the Medical Implant
Communication Service (MICS) band. The allowable channel                 capsule and so forth. Herein we will use the term electronic
bandwidth for this band is only 300 kHz. It is difficult to              pill to cover all these names. The early attempts were based
assign enough data rate for the high quality video data at the           on low frequencies and with simple structures [1][6]. A basic
moment for a real time monitoring. It is quite obvious that              transmitter using Collpitts or Hartley oscillator topology
there is a need for higher-bandwidth data transmission for               connected to a sensor has been used to send the signal from
electronic pills that could facilitate a better diagnosis.               inside the body to external devices for tracking physiological
   Wideband technology- (UWB communication) is an ideal                  parameters of inner organs. Despite simplicity, the early
physical layer solution that achieves a data rate equal or higher        systems were bulky due to large electronic components and
than 100 Mbps. Its current applications are mostly for in-door           batteries used and were targeting temperature, pH and
entertainment, radar and imaging. Due to high losses in body             pressure [8][9].
tissue at high frequencies many are skeptical about using                    As the electronic device should deeply be placed inside
UWB for implanted and, moreover, ingested devices. This                  the body, which makes the wireless communication
challenge can only be addressed by combined design of                    interesting due to its surrounding medium, the recent attempts
antennas, transmitters and receivers as described in this paper.         in electronic pills have also been limited to low frequency
In addition to reviewing and discussing the recent attempts in           transmissions (UHF-433 ISM or lower) [10]-[16]. The low




    M. R. Yuce and Ho Chee Keong ‘ work is supported by the Australian
Research Council (ARC) under Discovery Projects DP0772929.
 TABLE II.       RECENT RESEARCH PROJECT OUTCOMES ON ELECTRONIC PILL.

 Reference         Image              Image            Frequen.         Data       Modu-    Trans.        Physical        Power        Current
                   Resolution         sensor                            Rate       lation   Power         Dimension       Supply       Power

                                                                                                                                          NA
    (Thone,          640 X 480
                                       MT9V013           144 MHz        2 Mbps      FSK      -18 dBm      Not finalized     3V         (2 mW for
   2009)[14]           pixels
                                        (VGA)                                                                             coin cell       Tx)
                                                                                                                          2X 1.5 V
                      307,200            VGA,                            267                               11.3X26.7                   8 mA (24
  (Chen, 2009)                                           433 MHz                    FSK         NA                         silver-
                       pixels            0-2 fps                         kbps                               mmxmm                         mW)
      [10]                                                                                                                 oxide
    ( Wang,          510X480                                                                   High         10x190          3 V,
                                        PO1200              NA           NA                                                            125 mW
   2008) [13]          pixels                                                       AM       (variable)     mmxmm         wireless
                                         CMOS
    (Kfouri,         768 X 494            CCD                            250                                20X100         Li-ion
                                                            UHF                                 NA                                        --
   2007)[16]           pixels          ICX228AL                          kbps        --                     mmxmm          battery
  (Park, 2002)       510X492            OV7910                                                               10 X 7
                                                         315 MHZ         NA         AM          NA                                       NA
      [13]             pixels            CMOS                                                               mmxmm            5V
                                                                                                                           2X1.5 V
  Johannessen,                        Sensory: pH                                                           12X36
                   pH and Temp.                          433 MHz        4 kbps      OOK      NA, 1m                         SR48       15.5 mW
   2006) [11]                          and Temp.                                                            mm, 8g
                                                                                                                            Ag2O
                                                                                                                             3-V
   Valdastri,                                                                                5.6 mW        27X19X19
                   Multi-channel         Sensors         433 MHz        13 kbps     ASK                                    coin cell      --
   2004 [12]                                                                                   5m            mm3
                                                                                                                          (CR1025)
    Mackay,          pH, temp.,                                                                                               --
                                         Sensors          100 kHz         --         FM          --            --                         --
    1957 [1]        oxygen level
 The highlighted section is for visual based electronic pill systems.

frequency transmission is easy to design and is found                             data rate are desired for the purpose of low-power
attractive due to its high efficiency. However a low frequency                    consumption and miniaturization.
link requires large electronic components such as capacitors                          Another type of capsule is the robotic endoscope [13]
and inductors, which makes it difficult to realize a complete                     which additionally has features such as locomotion and the
integrated system.                                                                energy transmission using electromagnetic coupling.
     After recent significant technology improvements, design                     Although the device size is quite large comparing to other
of small size camera and battery could have been possible.                        proposed systems, it is probably because of these additional
Thus in the last ten years some research projects looking at                      functionalities. Similar to smartpill, such a device can be
developing electronic pills have concentrated mostly on the                       used for precise drug delivery in the human gastrointestinal
visual sensor system. Thus a high frequency link is required                      tract. Real-time energy transfer is necessary for these types of
for better resolution and a miniaturized system. Recent                           endoscopes to provide mechanical function as they require
telemetry systems being developed for the electronic pill                         large power for continuous movement.
technology are summarized in Table I. All these systems are                         A recent study [14] demonstrated a prototyping system to
still at prototype levels.                                                        achieve high data rate (2 Mbps) for higher image resolution.
     In [10], a wireless endoscope system uses a commercial                       It can enable an image resolution up-to 15-20 fps (frame per
RF transceiver operating at 433 MHZ ISM with 267 kbps.                            second) using compression technique like JPEG. It uses a
The electronic pill includes a passive wireless link used for                     simple Colpitts oscillator. The transmitter itself thus
wake-up to reduce power consumption. The wake-up system                           consumes low-power. However the actual power
recovers energy from a 915 MHz RF modulated signal with                           consumption of a device could only be realistic when all
some sort of identification code. This capsule does image                         blocks of an electronic pill are integrated together. The device
compressing techniques using an ASIC to enable higher                             operates at 144 MHz, relatively lower than most of the
transmission rate of images for low–data rate systems.                            systems that are operating at UHF, which necessitates a larger
     The pill in [11] uses a simple OOK wireless system.                          antenna that will increase the physical size. In [15], Park, et
Similar to the early developments, this device transfers the                      al. also uses a simple AM (amplitude modulation). It is
physiological data- pH and temperature. Another such device                       designed with a mixer and an oscillator circuit together with
was developed by Valdastri, et al., in [12] with a multi-                         the CMOS image sensor and a loop antenna to form a
channel feature to cover few different physiological                              capsule-shaped telemetry device. This device uses an external
parameters. It was tested in vivo in pigs using pressure                          control unit to control the capsule inside the human body.
sensors. The transmission range was reported as 5 m. These                             Another category of electronic pill technology is to use
devices do not require high data rate comparing to the video                      fluorescence spectroscopy and imaging, similar to those that
based electronic pills highlighted in Table I because                             are commercially available. Kfouri, et al., studied a
physiological parameters like pH and temperature are low-                         fluorescence-based electronic pill system that uses UV light
frequency signals. Simple modulation schemes like On-Off                          with illumination LEDs to obtain clearer images [16]. This is
Keying (OOK) and Amplitude Shift Keying (ASK) with low-                           like flash based digital camera widely used by people. Due to
the use of power hungry LEDS, such a device consumes                    from the Food and Drug Administration (FDA). The device
power higher than the other available systems. An alternative           contains 6 LEDs with adjustable illumination to maintain
power source together with battery is required to support the           optimal imaging. Currently all the video based commercial
electronics continuously. A wireless power, from outside to             systems being designed are based on illumination. The
inside, has been suggested. Although not specified, it                  electronic pill by SmartPill is designed to measure pressure,
probably used UHF frequency as the RF transmission.                     pH and temperature as it passes through the GI tract. A
    From Table I, it seems that in current attempts the                 receiving device worn by the patient collects data which is
transmission frequency has been limited to around UHF                   later examined by a physician. With information obtained
frequencies. Although the advances in high frequency and                from public domain, these pills are described in Table II.
high bandwidth communication technologies for wireless                      Due to the limited transmission bandwidth used for the
systems have been significant in the commercial domain,                 electronic pills that are currently being developed or the ones
these technologies are not directly transferable to biomedical          commercially available, the image transfer rate has been
implant or ingested systems due to the differing power, size,           limited to 0-10 frames per second. As high definition cameras
and safety related radiation requirements. As an example, in            are continuously being developed, they will be attractive for
[17] an implant prototyped with a ZigBee compliance –one of             use in electronic pill. However, a higher pixel camera will
the low-power, less complex and small size commercially
                                                                        require higher image transfer rate. As an example, if 1920 x
available wireless standard occupies an area of 26X14X7 mm3
without being integrated with other required blocks of an               1080 pixel (2 megapixel) charge-coupled device (CCD)
electronic pill. The existing advanced wireless systems such as         sensors to be integrated in an electronic pill, it will require a
ZigBee (IEEE 802.15.4), WLANs, and Bluetooth (IEEE                      data rate of 33.2 Mbit/frame, considering 2 Bytes are used per
802.15.1) operate at 2.4 GHz ISM band and suffer from the               frame. Currently such a high data rate is not possible with any
strong interference from each other when located in the same            of the available telemetry systems in electronic pills. If the
environment [18]. Thus an electronic pill should probably               allowable bandwidth used with UHF frequencies, transmission
have a different transmission band for an interference free             of this data rate will only give a transmission time of 10s or
wireless system. The existing wireless modules contain                  more per frame which will result in very small motion for a
complex multi-access communication protocols such as                    video streaming. Although compression techniques could be
OFDMA that increase the power consumption and size of the               used to some extend, it reduces the image equality. Thus in
wireless chip. Unless these chips are miniaturized to levels            future, a dedicated frequency band with larger bandwidth is
that can be inserted into a capsule size of 11mmX30 mm, the             required for high definition image transmission.
telemetry used will still be based on simple communication                  Since miniaturization is important, different design
modulations like ASK, OOK, FSK, AM.                                     approaches have been followed by the designers. Fig. 2
    Table II summarizes the commercially available electronic           illustrates different shapes that has been used or can be used
pill technologies that are already been used in clinical                to integrate all the necessary blocks. As shown, each unit can
environments. Current wireless endoscope device by “Given               be designed on a separate board layer and then stacked on top
Imaging” is used to diagnose disorders such as Crohn's
                                                                        of each other. In a design shown in Fig. 2-(a) antenna can be
disease, Celiac disease, benign and cancerous tumors,
                                                                        placed such that it can easily be inserted on top of the
ulcerative colitis, gastrointestinal reflux disease (GERD), and
Barrett's esophagus [4]. The pill uses the Zarlink’s RF chip for        transmitter layer. The capsule shape is also divided into two
wireless transmission [5]. The chip uses the MICS band that             regions where antenna can be designed to be placed in upper-
allows channels with only 300 kHz. It is thus difficult to              half whereas the remaining electronic units are packed in the
assign enough data rate for the high quality image and video            lower-half. Placing electronic units on one side of antenna is
data at the moment for a real time data transfer and                    another possibility (Fig. 2-(c)). Commercially available mini
monitoring.                                                             cameras can easily be integrated with electronic pills [19].
    RF Norika by RF system lab has a wireless power                     Small miniature rechargeable battery technologies are also
capability and localization capabilities. Another endoscope             being developed [20] with a dimension around 5 mm and can
EndoCapsule was developed by Olympus was mainly used in                 easily be integrated in a capsule structure shown in Fig. 2.
Europe. However in 2007 it has received marketing clearance

    TABLE II. COMPARISON OF HARDWARE DESIGNS FROM VENDORS, www.givenimaging.com, http://www.olympus-europa.com/endoscopy/,
    www.rfsystemlab.com, www.smartpillcorp.com.

    Model          Company       Camera            Freq.       Data         Power      Physical          Image rate and
                                 (Sensor)          (MHz)       Rate         Source     Dimension         resolution
    PillCam (SB)                                   402-405      800                                        14 images per
                      Given                                                               11X26
                                 Micron, CMOS       & 433       kbps        Battery                       second, or 2,600
                     Imaging                                                            mmxmm, <4 gr
                                                   (Zarlink)   (FSK)                                        color images
    EndoCapsule    Olympus       CCD camera,                                                11X26           2 images per
                                                      --           --      Battery
                   Optical       1920 X 1080                                               mmxmm               second
    Norika          RF System      CCD Image                                Wireless        9X 23
                                                      --           --                                           NA
                       Lab            sensor                                Power          mmxmm
    SmartPill        Smartpill     acidity (pH),                                            13X26           Only sensor
                                                      --           --       Battery
                      Corp.        press., temp.                                           mmxmm            discrete data
                                                                      printed antenna presented herein demonstrates good matching
                                                                      in the frequency band of 3.5-4.5GHz and the radiation
                                                                      performance has been evaluated experimentally using the I-
                                                                      UWB transmitter/receiver prototype to show that it is suitable
                                                                      for an electronic pill. The antenna matching has been
                                                                      optimized using CST Microwave Studio, commercial
                                                                      electromagnetic simulation software. Proposed antenna is
                                                                      printed on a 0.5mm thick RO4003 capsule-shaped, low loss,
                                                                      dielectric substrate ( ε r = 3.38 ). It can easily fit inside a
                                                                      size-13 capsule. Overall length and width of the antenna is
                                                                      28.7mm and 14mm, respectively. The antenna has been
Fig. 2. Possible physical shapes for electronic pills                 optimized using simulations and printed on one side of the
                                                                      substrate together with a Grounded-CPW (Coplanar Wave
       III.    IW-UWB TELEMETRY FOR ELECTRONIC PILL                   Guide) feed as shown in Fig. 4.
                                                                           Several transmitters have been designed to generate UWB
    Although the image based electronic pill systems listed in        signals. Short pulses are mainly generated according to the
Table I & II can provide some level of accuracy, for some             OOK and Pulse Position Modulation (PPM) modulated signal.
diseases detailed images may be required [21]. Thus a better          At the transmitter, the pulse generator unit produces a
resolution camera will be used. In order to monitor high              rectangular- shaped pulse with 1ns width (Fig. 3-(a)). The
quality images in real-time, a wideband radio link will be            spectrum of the rectangular pulse extends over an unlimited
desired for a high capacity data transfer and thus improved           frequency band. Thus a Band Pass Filter (BPF) centered at 4
image resolution [14][22]. A wideband, high frequency                 GHz with 1 GHz bandwidth is used to constrain the signal
technology will especially be useful for high definition images       power under the Federal Communications Commission (FCC)
exceeding 2 megapixels (i.e. > 1920 x 1080). Although there           emission mask (i.e. a band limited UWB system). The energy
have been ongoing advancements in UWB communication for               of the side lobes is maximized within the bandwidth of the
short range applications; they cannot directly be applied to          bandpass filter. The filtered pulses are fed into our custom
electronic pill technology because of different design and            made UWB antennas, shown in Fig. 3 and 4.
optimizations required due to stringent physical constraints               The receiver can easily be designed for a high data rate as
and biological safety. In the following section, we will study        it is built from off-the-shelf high performance RF components
the feasibility of wideband technology for electronic pills.          by using high performance RF ICs (i.e. Amplifiers, Mixers)
    The important parameters of the wideband technology are           and high speed Field Programmable Gate Arrays (FPGA).
its low power transmitter design, low-interference effect in          There are different receiver architectures that can easily be
medical environment and high data rate capability. The design         constructed. Usually a mixer is used to down convert the high
of a UWB wireless chip has been difficult for chip designers          frequencies to low frequencies. Herein a diode is used due to
due to the difficulty in the demodulation of narrow pulses with       simplification in the successive blocks. The received UWB
a low signal power level. Generally a UWB receiver circuit            signal is passed through a BPF, whose center frequency is 4
has demonstrated power consumption higher than that of a              GHz, to eliminate possible interference from the frequencies
narrow band system. One way to eliminate the high power               of WLAN standards (for example 2.4 GHz and 5 GHz). The
consumption of an ultra wideband transceiver is to use a              signal is then amplified by the Low Noise Amplifier (LNA). A
transmitter only in the electronic pill that will not need a signal   diode and a Low Pass Filter (LPF) down converts the UWB
from external unit to the electronic pill in the body.                signal and the baseband data is finally recovered by the
    The use of wideband technology for medical implants               FGPA. At the receiver end, the main component is the diode
should overcome unique challenges associated with the high            detector. When small input signals below -20dBm are applied
frequency implementation. To address these challenges, as             to the diode, it translates the high frequency components to
preliminary work in this study, we present a complete                 their equivalent low frequency counterparts due to its
                                                                      nonlinear characteristic. Measurement results, shown in Fig.
working UWB prototype with a capsule-shaped antenna
                                                                      3(b) are spectrum plots at the outputs of the receive antenna
specifically designed for the targeted application. The               and the low-noise amplifiers.
selected band is 3.5-4.5GHz (i.e. band-limited), which avoids              UWB prototype is capable of supporting a low-power
narrowband systems operating in the ISM bands. The initial            UWB communication, which will be ultimately used to form
design has been tested in a laboratory environment                    an in-body-to-air link, without violating FCC regulations.
demonstrating that an impulse-based UWB system is an                  Antennas were placed inside a plastic container. Prior to each
attractive design for wireless endoscope monitoring. The              measurement, jacket of aluminum foil covered the outer
result shows that with UWB signals it is possible to transmit         surface of the container to minimize outside coupling paths
data at a rate of 100 Mbps.                                           between the antennas.
    The prototype system used in the experiment is shown in                First measurement was taken inside the empty container
Fig. 3, with transmitter and receiver waveforms shown                 and the second with a meat sample inside. Measured S21
explicitly. A low-cost, printed, capsule-shaped UWB antenna           using the VNA is shown in Fig. 5. Coupling between antennas
has been designed for the targeted application [23]. The              in the same laboratory environment and instrument calibration
Fig. 3. A ultra wideband (UWB) wireless telemetry prototype and measurement results,(a) transmitter with 1 ns UWB pulse, and (b) receiver with spectrums.


                                                               Flange
                                                                                  transmission feasible for electronic pills, we propose to use
                    Y
                               R 1.75
                                                                                  higher transmitted signal levels at the transmitter. The UWB
                                                        0.50                      signal power is arranged such that when the signal is radiated
                                                                   50 Ohm Probe
                                          R 1.00                     Connector    through the skin, the power level should meet the FCC mask.
                 4.00
                                                                                  Considering the strong attenuation through the body tissue, the
                                                                                  transmitter power level will be adjusted from -20 dBm to 20
                                                                                  dBm in our system, without violating safety requirements.
  5.00




                                        8.00




             2.64                                                  1.65               Unlike the other designs, in our approach, the implanted
                 1.14
                                                   X
                                                                                  device does not contain a receiver. The transmission is one
                                                                      UWB
                                                                                  directional as the information needs to be recorded and
                        2.64
                                                                   Transmitter    monitored only. This simplifies the complexity of the device
          1.29




                                                                                  and increases its battery lifetime. When more than one
                                 4.70
  5.00




                                                                   CAMERA/
                                                                   SENSORS        electronic pill is used in the same environment, an individual
                                                                 Battery/Power
                                                                                  device ID (PN code) will be used in the transmitted signal to
                                                                 Management       eliminate interference between two devices or other UWB
                                               R 7.00                             devices [24]. As we only need a transmitter design for the
                                                                                  implanted system, the transmitter power consumption and
                                                                                  complexity will be traded off with that of the receiver as the
Fig.4 . A wireless electronic pill system with antenna dimensions.                receiver is located outside and its power consumption and size
for both through the meat and free space, are shown for                           are not crucial.
comparison. There is about 20-30 dB attenuation through meat                          Receiver circuits implement power hungry analog blocks
within 3-5GHz band for every 2 cm. This attenuation is not                        like LNA and mixers at the front-ends. Using only a UWB
only due to absorption by meat but also due to the antenna                        transmitter, analog blocks of commerical transceivers are
mismatch due to presence of meat also contributes to this.                        avoided in our electronic pill approach, which not only
Furthermore, high gain antennas systems with large aperture                       increases the battery life but also reduces the physical size.
can be used at the receiver unlike the one in the miniature pill.                 Using this approach a UWB telemetry link has been tested
Subsequently, the overall gain of the system will be improved                     over a 0.6 m across the laboratory both in free-space and when
to counter the attenuation by tissue.                                             loaded with meat emulating an implant once a high gain
    For a UWB transmitter, the regulation requires the signal                     antenna is used at the receiver site instead of one shown in
output to be -41 dBm/Hz or lower. To make UWB                                     Fig. 4. Using a high gain antenna at the receiver we could
reduce the tissue effect by 20 dB and more [23]. The 50 MHz                                systems for medical professionals to analyze real-time video
data stream is obtained at the FPGA after the demodulation                                 and image data wirelessly as a less invasive method.
process. The time domain signals before and after the FPGA
are shown in Fig 6. The recovered signal is a 50 Mbps pulse                                                                REFERENCES
obtained from UWB pulses with width of 1ns.
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Integration of antenna with the UWB transmitter electronics                                       http://www.smallbattery.company.org.uk/hearing_aid_batteries.htm.
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it is known that tissue imposes strong attenuation at higher                                      Crohn’s Disease,” US Gastroenterology Review 2005 - April 2005.
                                                                                           [22]   C. Kim, T. Lehmann, S. Nooshabadi and I. Nervat, “An ultra-wideband
frequencies, we have shown there are some advantages to use                                       transceiver architecture for wireless endoscopes,” International Symp.
wideband technology.                                                                              Commun. and Information Tech., pp. 1252-1257, 2007.
   Due to the high data rate capacity (e.g. 100 Mbps), a                                   [23]   T. Dissanayake, M. R. Yuce and Ho C. K. “Design and evaluation of a
wideband electronic pill can transmit raw video data without                                      compact antenna for implant-to-air UWB communication,” IEEE
any compressing, resulting low-power, less delay in real-time                                     Antennas and Wireless Prop. Letters, vol. 8, Page(s):153 - 156, 2009.
and increased picture resolution. With a high definition                                   [24]   N. Aydin, T. Arslan, and D. R. S. Cumming, “Design and
                                                                                                  implementation of a spread spectrum based communication system for
camera such as 2 megapixels, UWB telemetry can send up to                                         an ingestible capsule,” IEEE Trans. Information Technology in
10 frame per second (fps). We believe that the wideband pill                                      Biomedicine, Vol.9, March 2005.
technology is going to open up a new set of diagnostic

				
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